There are many types of welding power supplies and welding processes, such as short circuit, globular, spray or pulsed spray welding. Short circuit transfer welding generally consists of alternating between an arc state and a short circuit, non-arc state. During the arc state the wire melts, and during the short circuit state the metal further melts and the molten metal is transferred from the end of the wire to the weld puddle. The frequency of the process is determined by the welding parameters, and cannot be independently controlled.
Pulsed spray welding consists of pulsing the current output and intermittently "spraying" molten metal into the weld puddle. The output current is generally pulsed, at a controllable frequency, between a peak time and a background time. Generally, during the peak current time the wire melts, forms a ball, and the ball is transferred. The puddle cools during the background current time.
It is desirable to have consistent arc starting in most welding processes. The size of the ball at the end of the wire (formed when the last weld was terminated) is a significant factor in determining the amount of energy needed to initiate the arc. Thus, the condition of the end of the wire (size of the ball) from the previous weld should be consistent to provide consistent arc starting.
However, the size of the ball can vary from 1 to 3 times the diameter of the wire after a typical short circuit transfer welding process has ended. Previously, sometimes an operator cut the end of the wire, which eliminated the ball, or in some prior robotic arc spray systems an extra step to dress or trim the wire at the end of each weld and to insure the wire isn't frozen to the welded joint at arc end is provided (U.S. Pat. No. 5,412,175 issued May 2, 1995, e.g.). While this may produce a uniform wire diameter at the start of the next weld, it wastes time, and the extra step would not be needed if the wire had a consistent diameter when each weld is stopped.
There have been attempts in the prior art to control the termination of a welding process. A BETA-MIG.RTM. has used a predetermined "crater" for the stops. However, the BETA-MIG.RTM. did not provide a fast enough response, or an adequate control scheme, to produce the consistent ball size desired for short circuit transfer welding.
Another prior art system is in the Miller 60M.RTM. pulsed spray process, which has an algorithm that reduces the output pulse frequency to match the stopping of the motor. A final pulse is sent which blows one last ball off the wire and extinguishes the arc. However, this method will not work for processes such as short circuit transfer welding, that do not tightly control the frequency of the output power. Also this prior art does not desirably compensate for irregularities in the process, such as unintended shorts.
Accordingly, a power source and controller that provide a stop algorithm that reduces the size of the ball to be about that of the wire diameter, or of a size that allows consistent starts to be made, i.e. not a large ball, when the process is terminated, is desirable. This process will, preferably, insure that the wire is not frozen to the weld joint at arc end. Also, the stop algorithm should preferably be robust (i.e. able to function even during irregularities in the process) and adaptable for a variety of processes, such as MIG processes, spray processes, pulsed spray processes, or short circuit transfer processes.